The Bike-ID number is the unique Bikemember number printed on the sticker you place on your bike. When you buy a Bikemember subscription, you receive stickers for your bikes free of charge. If you later need additional stickers, you can always order them by signing in to My Page. You only need one sticker per bike.
How to register the sticker: See the step-by-step guide on the page Register your Bike ID (sticker).